Method and apparatus for monitoring particle laden pneumatic abrasive flow in an abrasive fluid jet cutting system

ABSTRACT

An abrasive jet cutting system may include a differential pressure measurement apparatus configured to measure a differential pressure between points in an abrasive supply system. The differential pressure may be used to determine one or more conditions of the jet and the abrasive delivery. The measured differential pressure may be used in a feedback control system, feed forward control system, and/or an alarm or safety system.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefit of and priority under 35U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No.61/682,665, entitled “METHOD AND APPARATUS FOR MONITORING PARTICLE LADENPNEUMATIC ABRASIVE FLOW IN AN ABRASIVE FLUID JET CUTTING SYSTEM,” filedAug. 13, 2012, assigned to the same assignee as the present applicationand which is incorporated herein by reference in its entirety.

BACKGROUND

Pneumatic conveyance of particles is used in a wide range of processesworldwide. One process that uses pneumatic conveyance of particles isassociated with abrasive fluid jet systems, which may be used inproduction cutting applications. Abrasive fluid jets are used to cut,drill holes through, or machine relatively hard materials such as glass,stone, and metals. Abrasive fluid jet cutting generally operates using ahigh speed jet of fluid to project abrasive particles to erode aworkpiece. The high speed fluid jet is generated by using a highpressure pump to deliver high pressure fluid to a nozzle, where the highpressure is converted to a high velocity fluid jet. The vacuum of thejet is used to convey abrasive particles such as garnet to the cuttinghead where they are accelerated by the fluid jet in a mixing tube justdownstream from the water orifice.

Abrasive fluid jet systems typically depend on an uninterrupted flow ofabrasive particles from an abrasive supply system. If the flow of theabrasive particles is interrupted, cutting failure typically results.Cutting failures may be a reduction of cutting edge quality possiblyresulting in failure to separate the workpiece. This may result in lossof a machined part, waste of material, loss of machine time, or otherpotentially costly and time wasting effects. Therefore, it is desirableto provide a reliable abrasive flow monitoring system.

Unfortunately, many flow sensors suffer from erosion and/or otherdegradation effects when used to measure a flow including entrainedabrasive particles. Other flow sensors are too expensive. Sensors basedon measuring an absolute pressure or vacuum in an abrasive deliverysystem has proven to be susceptible to inaccuracies related toatmospheric pressure changes and/or other factors. Conventional sensingsystems associated with pneumatic conveying systems have often failed tomeet or only poorly meet needs for stability, durability, accuracy,reliability, and cost. What is needed is a reliable and cost effectivemethod to reliably monitor the abrasive flow that does not suffer fromrapid deterioration in a streaming abrasive environment.

SUMMARY

Abrasive particle entrained fluid jets may be used to perform a varietyof cutting and milling operations. Abrasive particles may be deliveredto a fluid jet via entrainment in air. Maintaining a steady flow ofabrasive particles for entrainment into the fluid jet is generallydesirable to achieve high quality results. Measuring the flow ofabrasive particles in the entrainment air is one aspect of maintaining asteady flow of abrasive particles for entrainment in the fluid jet. Theair velocity may be higher than the average velocity of the abrasiveparticles themselves. The flow of air around the entrained particlesresults in a pressure drop, also referred to as a change in partialvacuum, arising from differential aerodynamic drag around each of theparticles. The sum of aerodynamic drag may be correlated to the numberor concentration of particles entrained in the air. The correlation maybe determined for a range of operating conditions. A differentialpressure or differential partial vacuum between two or more points in anabrasive supply system may be used, optionally in combination with otheroperating parameters, to determine the condition of particle flow. Thedifferential pressure or partial vacuum may be used in a feedback orfeed forward control loop and/or may be used to inform an operator aboutthe operational status of the particle flow and thus the cuttingoperation.

According to an embodiment, a method for monitoring an abrasive fluidjet cutting system includes providing an abrasive to an abrasive fluidjet nozzle as abrasive particles entrained in air flowing through anabrasive supply tube; and measuring a differential pressure between atleast two points along the abrasive supply tube to infer or determine anabrasive flow rate or abrasive flow condition.

According to another embodiment, a particle conveyor includes a particlesupply tube configured to pneumatically convey particles from a particleinlet port to a particle outlet port configured to be drawn down to apartial vacuum. The particle supply tube includes at least twomeasurement ports at different distances along the particle supply tubewith no flow constriction between the at least two measurement ports. Adifferential pressure transducer or two pressure transducers coupled tothe at least two measurement ports are configured to measure adifferential pneumatic pressure between the at least two measurementports. A controller operatively coupled to the differential pressuretransducer is configured to determine one or more particle flowparameters responsive to the differential pneumatic pressure.

According to another embodiment, a differential pressure measurementfitting for an abrasive jet cutting system includes a wall defining asmooth abrasive flow channel configured for air-entrained abrasive flowand at least two pressure measurement ports arranged at differentdistances along the abrasive flow channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an abrasive fluid jet system, according to anembodiment.

FIG. 2 is a diagram showing a relationship between the abrasive supplysystem and controller of FIG. 1, according to an embodiment.

FIG. 3 is a diagram of a portion of the abrasive delivery tube of FIGS.1 and 2 including a fitting with differential pressure measurementpoints, according to an embodiment.

FIG. 4A is a side sectional view of an abrasive inlet port, according toan embodiment.

FIG. 4B is a cross-sectional view of the abrasive inlet port of FIG. 4A,according to an embodiment.

FIG. 5 is a flow chart illustrating operation of an abrasive jet cuttingsystem with a differential pressure abrasive flow measurement, accordingto an embodiment.

FIG. 6 is a flow chart showing a method 601 for monitoring an abrasiveentrainment fluid jet, according to an embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented here.

FIG. 1 is a diagram illustrating a fluid jet cutting system 101configured to cut a workpiece 102, according to an embodiment. Acomputer interface 104 may be configured to receive computerinstructions corresponding to a cutting path through the workpiece 102.A controller 106 may be configured to receive the computer instructionsto drive the fluid jet cutting system 101. Alternatively, the cuttingpath may be produced by nozzle motion and/or workpiece motion driven bya different method, such as by hand guiding, for example.

The controller 106 may be operatively coupled to a high pressure pump108 via a pump interface 109. The pump 108 may optionally be controlledseparately. The high pressure fluid pump 108 is configured to providehigh pressure fluid through high pressure tubing 110 to a nozzle 112.The nozzle 112 receives the high pressure fluid and projects a highvelocity fluid cutting jet 114.

The controller 106 is operatively coupled to drive an actuation system116 configured to drive the position of the nozzle 112 via an actuationinterface 117. Typically actuation systems 116 include at least X-Ydrive. Some actuation systems additionally include Z-axis and tiltingaxes. The controller 106 drives the actuation system 116 to position thenozzle 112 to scan the fluid jet 114 across the workpiece 102 to makecuts. The workpiece 102 can be supported by a workpiece support system118 including bed slats 122 over a pool of water 120. Other embodimentscan include a fixed cutting head with an actuated workpiece.

A particle supply system 124 may provide abrasive particles such asgarnet entrained in air to the nozzle 112 through abrasive particlesupply tube 126, and particularly to a mixing tube (not shown). At themixing tube, the high velocity jet 114 draws a partial vacuum at anoutlet port of the abrasive supply tube 126, which creates a pneumaticdriving force to drive particles through the abrasive particle supplytube 126. The high velocity jet entrains the air containing the abrasiveparticles. The abrasive supply system 124 (of which the abrasive supplytube 126 may generally be considered to be a part) includes at least onesignal transmission path 128 configured to couple the abrasive supplysystem 124 to the controller 106. The signal transmission path 128 maybe configured to transmit a differential pressure signal from theabrasive supply system 124 to the controller 106.

An optional alarm output 130 may provide an apparatus for alerting auser of one or more operating and/or fault conditions. For example, thealarm output 130 may include a bell, speaker, beeper, buzzer, or otheraudible output selected to call attention to a fault condition.Alternatively or additionally, the alarm output 130 may include avisible indicator such as a computer display, a gauge, an indicatorlight, a strobe light or other visible output selected to call attentionto a fault condition. The alarm output 130 may also generate or cause tobe generated a display or transmission of an electronic message to callattention to a fault condition. The controller 106 may be configured toprovide an alarm signal to the alarm output 130 via a signaltransmission path 132. Optionally, the interface 104 may provide aninterface to an alarm output 130 and a separate signal transmission path132 may be omitted.

FIG. 2 is a block diagram of a subsystem 201 showing a relationshipbetween components of the abrasive supply system 124 and controller 106of FIG. 1, according to an embodiment. An abrasive hopper 202 may holdabrasive particles 204. The abrasive hopper 202 may, for example, beheld substantially at atmospheric pressure, or alternatively may be heldunder vacuum or at an elevated pressure. Abrasive particles 204 aremetered from the abrasive hopper 202 through a metering apparatus orvalve 206 that controls the rate of flow. According to an embodiment,the metering apparatus or valve 206 may be a predetermined length oftube at a predetermined diameter that allows a relatively constant rateof abrasive flow; using an effect similar to the neck of an hourglass.Optionally, the metering apparatus or valve 206 may be controlled by thecontroller 106 through a signal interface (not shown).

The abrasive particles may next flow through an optional shut-off valve208 that is optionally actuated by the controller 106. According to anembodiment, the abrasive particles 204 fall from the metering apparatusor valve 206 and the optional shut-off valve 208 under gravity throughan optional air gap 210 and into an abrasive inlet port 212 that isoperatively coupled to the abrasive supply tube 126. An embodiment ofthe abrasive inlet port 212 is shown in more representative form inFIGS. 4A and 4B.

In alternative embodiments, the abrasive particles 204 may be pulledfrom the abrasive hopper 202 under gravity, responsive to a screwconveyor, vacuum, pressure, or other abrasive introduction mechanismcorresponding to the apparatus 206, 208, 212 between from the abrasivehopper 202 and the abrasive supply tube 126. The controller 106 maycontrol such alternative apparatuses responsive to the measurement ofdifferential pneumatic pressure described herein.

According to an embodiment, the metering apparatus or valve 206 caninclude a mechanism such as a variable aperture to constrain the passageof abrasive particles. For example, the metering apparatus or valve 206may include a slide (not shown) configured to vary the size of a gapthrough which abrasive particles 204 are metered. The shut-off valve 208may be also be embodied as a slide valve, or may be embodied as abladder valve, for example. Optionally, the shut off valve 208 may beomitted and on/off functionality may be provided by the meteringapparatus or valve 206.

After entering the abrasive supply tube 126 at the abrasive inlet port212, the abrasive particles are entrained in air moving through theabrasive supply tube 126 and are pneumatically conveyed as entrainedparticles through the abrasive supply tube 126 to an abrasive outletport (not shown) that opens into a nozzle mixing tube (not shown).

The air moving through the abrasive particle supply tube 126 movesfaster than the particles entrained in the air. This “blows” theparticles through the abrasive supply tube 126. Typically, frictionaleffects of the air moving past and around the abrasive particles causesa pressure drop. A larger amount or concentration of abrasive particlesin the abrasive particle supply tube 126 causes a higher pneumaticpressure loss. Thus, the pressure drop through the abrasive supply tube126 is indicative of the flowing condition and flow rate of theentrained particles.

The pneumatic pressure loss in the abrasive supply tube 126 is measuredas a differential pressure between at least two points 216 and 218 alongthe abrasive supply tube 126. The first point 216 may correspond to afirst orifice and the second point 218 may correspond to a secondorifice located along the abrasive supply tube 126 between and notincluding the inlet port 212 or the abrasive outlet port (not shown).According to an embodiment, the first point 216 and the second point 218may be located along a fitting, as shown below.

A differential pressure transducer 214 is configured to measure thedifferential pressure between the first 216 and second 218 orifices.Optionally, the differential pressure between the first 216 and secondorifices 218 may be measured by a respective first transducer and secondtransducer (not shown) that each measure an absolute or gauge pressure.The respective absolute or gauge pressures may be converted to adifferential pressure by pressure comparison.

In some applications the distance between differential measurementpoints 216, 218 may be relatively small. According to an embodiment, themeasured differential pressure may be substantially attributable topressure drop created by air flow around entrained abrasive particles.In other applications, the distance between differential measurementpoints 216, 218 may be large and/or there may be an ell or anotherfitting between the measurement points 216, 218. According to anembodiment, the differential pressure may correspond to friction lossessubstantially created by a combination of airflow between the at leasttwo points and airflow around the entrained abrasive particles betweenthe at least two points.

Optionally, a sensor module 220 may receive the differential pressureelectrical signal and convert it to data that is transmitted to thecontroller 106 via the at least one signal transmission path 128.Alternatively, the sensor module 220 may receive first and secondabsolute or gauge pressure transducer electrical signals and convertthem to a differential pressure signal or data that is then transmittedto the controller 106. The differential pressure signal may include asignal and/or data transmitted between the sensor module 220 and thecontroller 106.

According to an embodiment, the pressure transducer 214 and the sensormodule 220 (or optionally an integrated portion of the controller 106)may further be configured to sense an absolute or average gauge pressurein addition to sensing a differential pressure.

The controller 106 may be configured to transmit one or more signalsthrough one or more interfaces 222 responsive to the pressuredifferential between points 216 and 218. For example the one or moreinterfaces 222 may include the pump interface 109, the actuationinterface 117, the signal transmission path 132 that interfaces with thealarm output 130, or the interface 104 shown in FIG. 1. Thus, thecontroller 106 may be configured to receive a differential pressuresignal from the abrasive supply system 124 and responsively control thesupply of fluid to the high pressure nozzle 112, movement of theactuation system 116 for the high pressure nozzle 112, operation of theabrasive supply system 124, providing an alarm from the alarm output130, and/or other responses or actions.

When the system or subsystem 101, 201 is starting up, differentialpressure between points 216, 218 may typically be quite low or otherwiseoutside a normal operating range. The controller 106 may be configuredto ignore the differential pressure during start-up.

During operation, the controller 106 may be configured to respond whenthe differential pressure signal indicates a decrease in differentialpressure below a predetermined value. According to an embodiment, thepredetermined value may be determined at least in part responsive to apreviously measured differential pressure. For example, changes arisingfrom variations in abrasive particle size, system wear, and otherfactors may be exhibited and monitored as gradual changes indifferential pressure that do not relate to fault conditions. Suchgradual changes may be tracked and used to monitor the system conditionuntil a value is reached which may result in a state at which thecontroller 106 responds with a fault response.

Optionally, the controller 106 may operate at least partially usingdigital logic, analog logic, and/or fluid logic. In the case of at leasta portion of the controller 106 including a fluid logic, thedifferential pressure transducer 214 (or alternatively the pair ofabsolute or gauge pressure transducers, not shown) may be omitted andthe differential pressure signal transmission path and/or the at leastone signal transmission path 128 may include pneumatic or vacuum linesrather than electrical conduction paths, wireless signal transmissionpaths, etc. In the case of a controller 106 that is at least partiallypneumatic, the differential pressure transducer 214 may be replaced byone or more diaphragms or filters configured to separate a “clean”pneumatic controller side from a “dirty” pneumatic conveying gas in theabrasive supply tube 126.

FIG. 3 is a side sectional view of a portion 301 of the abrasive supplytube 126 of FIGS. 1 and 2 including the differential pressure points216, 218, according to an embodiment. The abrasive supply tube 126 mayinclude a fitting 302. The fitting 302 may be referred to as adifferential pressure measurement fitting.

The fitting 302 includes walls that define a flow channel 304, having adiameter D, configured to provide a path for the flow of gas withentrained abrasive from a flow channel input 306 to a flow channeloutput 308. First and second pressure measurement ports 310, 314 may beconfigured to receive a differential pressure measurement transducer 214(or alternatively, respective absolute or gauge pressure transducers)shown in block diagram form in FIG. 2. Alternatively or additionally,the pressure measurement ports 310, 314 may be configured to receivepneumatic diaphragms, filters, and/or fittings for coupling to pneumaticsignal lines. The first and second measurement ports 310, 314communicate with the flow channel 304 via respective orifices 312, 316.

At the entrance 306 to the flow channel 304, the fitting 302 includes afirst coupling 318 configured couple the abrasive flow channel 304 toreceive air-entrained abrasive from an abrasive source, such as theabrasive supply system 124. At the exit 308 from the flow channel 304,the fitting 302 includes a second coupling 320 configured couple theabrasive flow channel to the rest of the abrasive supply tube 126.According to an embodiment, the first pressure measurement point 216 andcorresponding orifice 312 are situated at a position far enough awayfrom the input 306 to avoid perturbations in gas and abrasive flowarising from entrance effects.

The first and second orifices 312, 316 are arranged at differentpositions along the length of the flow channel 304 separated by adistance L. According to an embodiment, the orifices 312, 316 of thepressure measurement ports 310, 314 are configured to have similar orsubstantially identical flow restriction. The substantially identicalflow restriction may provide substantially identical entrance pressurelosses for the respective orifices 312, 316.

The differential pressure measured between the pressure measurementports 310 and 314 correlates with the amount (e.g., the concentration)of particles entrained between the pressure measurement ports 310, 314.The pressure drop is caused by a summation of frictional losses as airflows around each particle. For a system that is operating normally, thenumber of abrasive particles entrained between the pressure measurementports 310, 314 at any one time remains substantially constant. Thus, thedifferential pressure is indicative of the pneumatic air flow condition(e.g., the velocity of air) and the concentration of abrasive particlesin the control volume between the measurement ports. It is therefore ameasure of the condition of the airstream and the condition of abrasiveparticle delivery to the nozzle, which may also be indicative of theabrasive flow rate and the condition of the air flow producing venturisystem in the cutting head.

Notably, the fitting 302 does not include a conventional pressure dropconstriction such as a metering plate or a venturi. In such systems, thepressure drop is a function of the (fixed) geometry of a flowconstriction disposed between differential pressure measurement ports.Conventional differential pressure measurement fittings, for examplethat include a plate with a hole or a venturi through which gas flows,have a fixed geometry and hence a fixed pressure drop. However, suchconventional measurement fittings are not suitable to measuring flow ofa gas carrying entrained particles because the particles can causeexcessive wear on the fitting. In place of a flow constriction such as aplate or venturi, embodiments of the present invention use the presenceof the particles themselves to create a restriction for measuring thedifferential pressure. The gas (air) generally moves significantlyfaster than the particles. Thus, each particle can be modeled as astationary sphere with gas moving around it.

Optionally, absolute or gauge pressure may also be measured. Absolute orgauge pressure may be measured as the pressure at one or the other ofthe points 216, 218. Average (absolute or gauge) pressure may bemeasured by averaging the pressures measured at both points 216, 218.

FIG. 4A is a side sectional view of an abrasive particle inlet port 212,according to an embodiment. FIG. 4B is a cross-sectional view of theabrasive inlet port of FIG. 4A, according to an embodiment. Withreference to FIG. 2 and FIGS. 4A and 4B, the abrasive particles 204 fallthrough the air gap 210 onto a collection surface 302 of the inlet port212. According to an embodiment, the collection surface 302 is aV-shaped extension of the inlet port 212 and is sized to collect much orall of the falling abrasive particles 204. As shown, the collectionsurface 302 may be held at an angle selected to deflect the abrasiveparticles 204 toward an inlet port entrance 304. Vacuum produced at themixing tube (not shown) draws air into the inlet port entrance 304. Theinrush of air entrains abrasive particles 204 and also pulls theabrasive particles into the inlet port entrance 304.

The controller 106 may respond to changes in the differential pressureLIP in various ways, according to embodiments. FIG. 5 is a flow chart501 illustrating operation embodiment of an abrasive jet cutting systemdepicted in the illustrative embodiments of FIGS. 1 and 2. Beginning atstep 502, the abrasive jet cutting system, including at least the pump108 and the abrasive supply system 124, is started. During step 502, anon-steady state may exist in abrasive flow. The differential pressuremay therefore fluctuate as steady state abrasive flow is established.During step 502, the controller 106 may ignore the differential pressureAP or alternatively apply different set points and/or logic thatdetermine how to respond to changes in differential pressure AP.

When start-up 502 is complete, the system progresses to an operationstate 504. During the operation state 504, step 506 progresses, whereinabrasive is conveyed to the nozzle 112 through the abrasive supply tube126. Simultaneously, one or more pumps 108 are operated to provide highpressure fluid to the nozzle 112. The nozzle 112 includes a mixing tube(not shown). The high velocity movement of the fluid jet 114 produces apartial vacuum in the mixing tube. The partial vacuum in the mixing tube(where the output port of the abrasive supply tube 126 is located)creates a pressure differential driving force sufficient topneumatically convey the abrasive particles from the abrasive input portto the abrasive output port. The abrasive particles become entrained inthe high velocity jet 114 in the mixing tube (not shown). Optionally,step 506 may include opening a valve or operating a compressor toprovide abrasive conveying air.

In one embodiment, a pressure drop may be detected in step 508 in astate wherein abrasive is not flowing. This detection of the pressuredrop may provide information about the condition of the high velocityjet 114 without abrasives, which is information that can be useful tomonitor regularly.

Substantially simultaneously in a state wherein abrasive is flowing instep 506, step 508 progresses where the differential pressure AP ismeasured as described elsewhere herein. Optionally, differentialpressure AP measurement may be accompanied by an average, absolute, orgauge pressure measurement, which may provide additional informationabout operation of the system, as described above. Proceeding to step510, the measured differential pressure AP is compared to a set point ora range, and the existence or absence of a differential pressure APfault is determined. Optionally, step 510 may also include determinationof the existence or absence of an absolute, gauge, or average pressurefault.

As described above, the differential pressure AP decreases in responseto or when the velocity V decreases corresponding to a reduction in gasflow. Similarly the differential pressure AP decreases in response to orwhen the (variable) coefficient of friction decreases corresponding to areduction of abrasive in the gas.

If no differential pressure fault exists, the program returns tocontinue executing steps 506 and 508. The process 504 may continuesubstantially continuously while the system operates. The method orprogram 501 may, within the process 504, execute an explicit step 510 atan interval, or may alternatively operate according to interrupt logic.According to embodiments, the process 504 may be at least partlyembodied by or in software executed by a processor (such as by thecontroller 106 or other processor), firmware, and/or hardware.

If a pressure fault is determined to exist in step 510, the programproceeds to step 512 where the system is controlled responsive to thepressure fault. Step 512 may include correction of a problem, and/or mayrepresent providing an alert and/or shutting down at least portions ofthe abrasive jet cutting system. For example, controlling operation ofthe abrasive fluid jet cutting system 101 may include at least one ofcontrolling the pump 108 (e.g., shutting off the pump), controlling anabrasive supply system (e.g., stopping the flow of gas to the abrasivesupply system or refilling the abrasive hopper 202), controlling theactuation system 116 of the nozzle 112 (e.g., by moving the nozzle 112to a safe position such as to reduce the possibility of damage to aworkpiece 102), and/or controlling an alarm (e.g. outputting an alarmsignal via an alarm output 130 to alert a user of the fault condition).

If the differential pressure AP fault is corrected, as determined bystep 514, the process proceeds to step 516. Step 516 is a decision blockthat determines whether or not the system is running. For example step512 may involve refilling the abrasive hopper, modifying an abrasive gaspressure, modifying cutting parameters, or other response that does notinvolve shutting down the abrasive jet cutting system 101. In the casewhere the response to the differential pressure fault involves suchcorrective or adaptive actions, the program 501 may return to theprocess 504 where operation may continue substantially unimpeded.Alternatively, the system control provided in step 512 may involveshutting down all or a portion of the abrasive jet cutting system 101.If the system is at least partially shut down, the program 501 mayproceed from step 516 to step 502, where the system is started up again.

Optionally, step 508 may include writing differential pressure APvalues, or one or more parameters calculated therefrom, to differentialpressure data storage 518. The algorithm to determine the existence of adifferential pressure fault used by step 510 may read the differentialpressure AP values or parameters in the differential pressure datastorage 518 to determine the existence or absence of a differentialpressure AP fault. Values from the differential pressure data storage518 may be used to determine a differential pressure AP set point atwhich a fault is considered to exist. For example, a progression ofsmoothly increasing or decreasing differential pressure AP values may beattributed to normal wear, a gradual depletion of abrasive particles ina hopper, a change in abrasive grit, or other effects, and thedifferential pressure fault set point parameter may be modified in thedifferential pressure data storage 518 to accommodate such normalvariations in operating characteristics.

Values from the differential pressure data storage 518 may additionallyor alternatively be used to select from among possible controlalgorithms performed in step 512. For example, a differential pressureAP history and/or absolute, gauge, or average pressure history stored inthe differential pressure data storage 518 may be used to illuminate thenature of a differential pressure fault. For example, a gradual changein differential pressure AP may be indicative of a reduced abrasiveflowrate, and a control algorithm executed in step 512 may involvesimply alerting a user of a need to adjust the settings for the abrasiveflowrate. Alternatively, an abrupt change in differential pressure ΔPmay be indicative of a serious malfunction and drive a control algorithmexecuted in step 512 to perform a system shutdown.

Additionally, the algorithm performed during process 504 may beaugmented by information related to other operating parameters of thesystem. For example, a system shutdown or modification may be delayeduntil after completion of a cut or a workpiece.

FIG. 6 is a flow chart showing a method 601 for monitoring an abrasiveentrainment fluid jet, according to an embodiment. In step 602, asignificant value may be derived by compiling a relationship between ameasured pressure drop in an abrasive particle delivery subsystem and atleast one physical property or parameter of an abrasive cutting system.For example, deriving the significant value may include compiling arelationship between the measured pressure drop and an abrasive cuttingsystem water pressure. In another example, optionally used in amultivariate relationship along with water pressure, deriving thesignificant value may include compiling a relationship between themeasured pressure drop and an abrasive cutting system orifice diameteror mixing tube diameter.

Proceeding to step 604, the significant value may be monitored whileoperating the abrasive cutting system 101. Monitoring the significantvalue may include comparing the significant value with one or morepre-determined constant values to determine the condition of air flow inthe abrasive particle subsystem. Such an approach may be applieddynamically. For example, monitoring the significant value whileoperating the abrasive cutting system may include comparing thesignificant value with one or more predetermined constant values todetermine the condition and changes of the water jet. Additionally oralternatively, monitoring the significant value while operating theabrasive cutting system 101 may include comparing the significant valuewith the one or more predetermined constant values to determine thecondition and changes in abrasive flow rate. For example, this mayinclude comparing the significant value with the one or morepredetermined constant values to determine a flow rate of abrasiveparticles being carried by the entraining air.

The method 601 may also include a step of predetermining constant valuesfor comparison (not shown). The predetermined constant values may bedetermined in a variety of ways. For example, the method 601 may includedetermining the one or more predetermined constant values by measuringthe significant value at fixed conditions while the abrasive cuttingsystem is operating properly. This can provide a baseline against whichthe significant value is compared. Alternatively, the predeterminedconstant value may be calculated from physical properties and parametersof the abrasive cutting system. Similarly, the predetermined constantvalue may be determined by a combination of calculation from physicalproperties and parameters of the abrasive cutting system and bymeasuring the significant value at fixed conditions while the abrasivecutting system is operating properly.

A variety of additional steps may be performed responsive to themonitoring 604. For example, the method 601 may include displaying themonitored significant value and/or a predetermined reference value (notshown). Moreover, the method 601 may include generating a statisticalvalue corresponding to variations in the monitored significant value(not shown). The method 601 may also include analyzing the performanceof the abrasive cutting system by comparing monitored significant valuesor the statistical value corresponding to variations in the monitoredsignificant value against predetermined significant values.

Optionally, the analysis is performed by an abrasive fluid jetcontroller, such as the controller 106 shown in FIG. 1. Alternatively,the analysis may performed by a computer operatively coupled to theabrasive fluid jet controller via the data interface 104 (FIG. 1). Themethod 601 may also include actuating an alarm output (not shown) inresponse to or when the monitored significant value changes by an amountcorresponding to an alarm. the alarm may be output via the datainterface 104 and/or via an alarm 130 and/or via an alarm signaltransmission path 132 (FIG. 1), including electronic messages likeemail, SMS, and the like.

Optionally, the method 601 may include pausing the abrasive fluid jetcutter at a next convenient point or immediately stopping the abrasivefluid jet cutter (not shown) in response to or when the monitoredsignificant value changes by a corresponding amount.

While the transmission of signals and actions has been described aspositive signal transmission, other forms of data or signal transmissionmay be substituted. For example, referring to FIG. 2, the interfacebetween the sensor module 220 and the controller 106 may be configuredas a fail-safe interface where stopping the transmission of data or asignal corresponds to a fault condition. Referring to FIG. 1, similarinterfaces may be provided between the controller 106 and other systemcomponents such as the pump interface 109, the actuation interface 117and/or the signal transmission path 132 that interfaces with the alarmoutput 130 and may involve positive or negative data or signalconditions. Accordingly, transmitting a signal may include sending asignal or ceasing to send a signal.

Although the embodiments described herein may refer with some amount ofspecificity to an abrasive supply system for an abrasive jet cuttingsystem, the differential pressure measurement method (including adifferential pressure measurement fitting that includes no fixedpressure drop constriction) may be applied to the measurement of flow inother pneumatic particle conveyors. For example, solids materialhandling systems such as used in the cement and concrete industries,food production, and other industries may benefit from the flowmeasurement described herein.

The descriptions and figures presented herein are necessarily simplifiedto foster ease of understanding. Other embodiments and approaches may bewithin the scope of embodiments described herein. Embodiments describedherein shall be limited only according to the appended claims, whichshall be accorded their broadest valid meaning.

1. A method for monitoring an abrasive fluid jet cutting system,comprising: providing an abrasive to an abrasive liquid jet nozzle byentraining abrasive particles in air through an abrasive supply tube;and measuring a differential pressure between at least two points alongthe abrasive supply tube.
 2. The method for monitoring an abrasive fluidjet cutting system of claim 1; wherein measuring the differentialpressure between at least two points along the abrasive supply tubeincludes receiving pressures from at least two pressure measurementports formed in the abrasive supply tube at respective differentdistances between an abrasive entry point and the nozzle.
 3. The methodfor monitoring an abrasive fluid jet cutting system of claim 1; whereinthe at least two points include respective pressure measurement ports inone or more fittings disposed in the abrasive supply tube at a specifieddistance between each other.
 4. The method for monitoring an abrasivefluid jet cutting system of claim 1; wherein the measured differentialpressure is substantially attributable to pressure drop created by airflow between the measurement points and around entrained particles. 5.The method for monitoring an abrasive fluid jet cutting system of claim1, wherein the differential pressure corresponds to frictionsubstantially created by a combination of airflow between the at leasttwo points and airflow around the entrained abrasive particles betweenthe at least two points.
 6. The method for monitoring an abrasive fluidjet cutting system of claim 1, further comprising: determining acondition of the flow of the abrasive based at least in part on themeasured differential pressure.
 7. The method for monitoring an abrasivefluid jet cutting system of claim 1, further comprising transmitting acontrol signal in response to the differential pressure, whereintransmitting the control signal includes sending a signal or ceasing tosend a signal.
 8. The method for monitoring an abrasive fluid jetcutting system of claim 1, further comprising: determining a flow rateof the abrasive based at least in part on the measured differentialpressure; and/or determining the condition of the jet by measuring thedifferential pressure without abrasive flow
 9. The method for monitoringan abrasive fluid jet cutting system of claim 1, further comprising:measuring an average pressure, absolute pressure, or gauge pressure fromat least one of the two points along the abrasive supply tube.
 10. Themethod for monitoring an abrasive fluid jet cutting system of claim 1,further comprising: controlling operation of the abrasive fluid jetcutting system responsive to the measured differential pressure.
 11. Themethod for monitoring an abrasive fluid jet cutting system of claim 10;wherein controlling operation of the abrasive fluid jet cutting systemincludes at least one of controlling a pump, controlling an abrasivesupply system, controlling a nozzle actuator, controlling an alarm, anddisplaying or transmitting a notification.
 12. The method for monitoringan abrasive fluid jet cutting system of claim 1, further comprising:driving a pressure differential fault determination algorithm accordingto at least the measured differential pressure.
 13. The method formonitoring an abrasive fluid jet cutting system of claim 1, wherein thegas and entrained abrasive particles flow between the at least twopoints through a gas flow channel having substantially no flowconstriction.
 14. The method for monitoring an abrasive fluid jetcutting system of claim 1, wherein measuring a differential pressurebetween at least two points along the abrasive supply tube includesmeasuring a differential partial vacuum between the at least two points.15. The method for monitoring an abrasive fluid jet cutting system ofclaim 1, wherein measuring a differential pressure between at least twopoints along the abrasive supply tube includes measuring a change ofpartial vacuum between two points in the abrasive supply tube.
 16. Themethod for monitoring an abrasive fluid jet cutting system of claim 15,wherein measuring the differential pressure includes performing themeasurement with one differential pressure sensor.
 17. The method formonitoring an abrasive fluid jet cutting system of claim 15, whereinmeasuring the differential pressure includes performing the measurementwith two sensors and determining the difference in pressure or partialvacuum between the two sensors.
 18. The method for monitoring anabrasive fluid jet cutting system of claim 15, wherein the at least twopoints are at a fixed distance to one another along the abrasive supplytube and a fixed distance to an abrasive liquid jet cutting head. 19.The method for monitoring an abrasive fluid jet cutting system of claim15, wherein the abrasive supply tube between the at least two points hassubstantially the same surface properties and diameter as other regionsalong the abrasive supply tube.
 20. The method for monitoring anabrasive fluid jet cutting system of claim 15, wherein the abrasivesupply tube between the at least two points differs in at least one ofmaterial, shape, surface texture, or form compared to other regionsalong the abrasive supply tube.
 21. The method for monitoring anabrasive fluid jet cutting system of claim 15, wherein the two points inthe abrasive supply tube are disposed in physically separate componentsof the abrasive supply tube.
 22. The method for monitoring an abrasivefluid jet cutting system of claim 15, wherein the two points in theabrasive supply tube are disposed in a single physical piece of theabrasive supply tube.
 23. The method for monitoring an abrasive fluidjet cutting system of claim 1, wherein measuring a differential pressurebetween at least two points along the abrasive supply tube furthercomprises: measuring a plurality of differential pressures or partialvacuums between a plurality of pairs of points along the abrasive supplytube.
 24. A particle conveyor, comprising: a particle inlet port; aparticle outlet port configured to be drawn to a partial vacuum; aparticle supply tube configured to pneumatically convey particles fromthe particle inlet port to the particle outlet port, the particle supplytube including at least two measurement ports at different distancesalong the particle supply tube having no flow constriction between theat least two measurement ports; a liquid jet nozzle including a mixingtube configured to entrain the particles from the outlet port in a highvelocity liquid jet; a differential pressure transducer coupled to theat least two measurement ports and configured to measure a differentialpneumatic pressure between the at least two measurement ports; and acontroller operatively coupled to the differential pressure transducerand configured to determine one or more particle flow parametersresponsive to the differential pneumatic pressure.
 25. The particleconveyor of claim 24, wherein the particle conveyor comprises anabrasive supply system for an abrasive jet cutting system and theparticles are abrasive particles; and wherein the mixing tube isconfigured to draw the partial vacuum and entrain the abrasive particlesin a high velocity liquid jet in response to the liquid jet nozzle beingpressurized.
 26. The particle conveyor of claim 24, wherein the particleinlet port is held substantially at atmospheric pressure.
 27. Theparticle conveyor of claim 24, further comprising: a fitting forming aportion of the particle delivery tube, the fitting including a walldefining an entrained particle flow channel, and having at least twomeasurement ports separated by a length along the entrained particleflow channel; and wherein the differential pressure transducer isoperatively coupled to the at least two measurement ports.
 28. Theparticle conveyor of claim 27, wherein a differential pressure betweenthe at least two measurement ports is proportional to a pressure dropcaused by flow of air around and past entrained particles in theentrained particle flow channel between the at least two measurementports.
 29. The particle conveyor of claim 27, wherein the at least twomeasurement ports are at non-right angles relative to the entrainedparticle flow channel to reduce or eliminate particles entering themeasurement ports.
 30. The particle conveyor of claim 24, wherein thedifferential pressure transducer comprises: two or more absolute orgauge pressure transducers operatively coupled to respective measurementports.
 31. The particle conveyor of claim 24, wherein the controller isconfigured to operate using electrical, pneumatic, or electrical andpneumatic control logic.
 32. The particle conveyor of claim 24, whereinthe one or more particle flow parameters includes one or more of nominalparticle flow, a low concentration of entrained particles, or a blockagein particle flow.
 33. The particle conveyor of claim 24, wherein theparticle conveyor comprises an abrasive supply system for an abrasivejet cutting system and the particles are abrasive particles; and furthercomprising: a fluid jet nozzle including a mixing tube configured todraw the partial vacuum and entrain the abrasive particles in a highvelocity fluid jet in response to the fluid jet nozzle beingpressurized; and wherein the controller is configured to control atleast one selected from the group consisting of a supply of fluid liquidto the fluid liquid jet nozzle, movement of the fluid liquid jet nozzle,operation of the abrasive supply system, and providing an alarmresponsive to determining the one or more particle flow parameters. 34.The particle conveyor of claim 33, wherein the controller is configuredto ignore the differential pneumatic pressure or apply a differentresponse to the differential pneumatic pressure during start-up.
 35. Theparticle conveyor of claim 34, wherein the controller is configured torespond if one or more of the differential pneumatic pressure signalindicates a decrease in differential pneumatic pressure below a lowpressure value or the differential pneumatic pressure signal indicatesan increase in differential pneumatic pressure above a high pressurevalue.
 36. The particle conveyor of claim 35, wherein the differentialpneumatic pressure value or values is determined at least in partresponsive to one or more previously measured differential pneumaticpressures. 37.-57. (canceled)